1. Technical Field
The present invention relates in general to a method and system for reducing asymmetry and distortion in an output signal and in particular, to a method and system for reducing asymmetry and distortion in an output signal from a magnetoresistive sensor. Still more particularly, the present invention relates to a method and system for linearizing the output of a magnetoresistive sensor in a disk drive system.
2. Description of the Related Art
Magnetoresistive ("MR") sensors responsive to changes in resistivity brought about by the presence of magnetic fields are increasingly being employed as read transducers in magnetic disk drive heads mainly because the change of resistivity in such sensors is independent of disk speed, depending only upon the magnetic flux. A MR head is a magnetoresistive sensor that has a resistivity that is a function of the input flux. As the input flux increases, the resistance in the MR head decreases. The resulting MR resistance curve of the MR head resistivity is very nonlinear, and since the curve contains nonlinearities, the recording channel attached to the MR head will also contain distortions unless these nonlinearities may be compensated for.
One method of linearizing an output signal from a MR head involves utilizing analog circuits to compensate for the nonlinearities. For example, Jove, U.S. Pat. No. 4,706,138, discloses an analog circuit in FIG. 4 thereof for decreasing sensitivity to variations in the MR sensor resistance.
In accordance with an analog method of compensation, an operating point at the center of the most linear portion of the MR resistance curve for the MR head is the operating point usually chosen. The operating point is implemented in an analog circuit to linearize the output for a limited range around the operating point. One problem associated with this method is that component values in the analog circuit will drift with time. As a result, the analog circuit may no longer accurately linearize the output as time passes. Additionally, the MR resistivity curve for a particular MR head will also change over time. Consequently, outputs or different gains will result from changes in an MR head over time.
Furthermore, in a disk drive, many MR heads are normally switched into a single amplifier. Currently, the characteristics of multiple MR heads, i.e., gain, must be carefully matched. In attempting to match various MR heads, problems may occur if the signal sent to the amplifier from a MR head is too small or too large. For example, if the signal is too small, the amplifier may not increase the strength of the signal sufficiently, resulting in data errors. Additionally, too large a signal going into an amplifier will also cause errors in data retrieval. As a result, MR heads must be carefully matched such that all the MR heads in a disk drive have gains which are as close as possible to each other. Consequently, a MR head must often be discarded because its characteristics vary too far to be utilized with other available MR heads.
Therefore, it would be desirable to have a method and system for adaptively linearizing the output from a MR head while eliminating the problems associated with characteristics of components and the MR head itself changing over time.